1. Field of the Invention
The present invention relates to a liquid-droplet jetting apparatus which jets liquid droplets, and a liquid transporting apparatus which transports a liquid.
2. Description of the Related Art
Among ink-jet heads (liquid-droplet jetting apparatuses) which perform recording on a recording medium by applying pressure to an ink in a pressure chamber communicating with a nozzle to discharge the ink from the nozzle, there is an ink-jet head in which a vibration plate arranged to cover a pressure chamber is deformed by a piezoelectric actuator so as to apply pressure to an ink in the pressure chamber. For example, in an ink-jet head described in FIG. 3 of U.S. Patent Application Publication No. US 2005/0068376 A1 (corresponding to FIG. 3 of Japanese Patent Application Laid-open No. 2005-125743), a piezoelectric layer is formed on an upper surface of a vibration plate, and an upper electrode (individual electrode) is formed on a portion of an upper surface of the piezoelectric layer, the portion overlapping with a pressure chamber. Further, the ink-jet head performs a so-called pushing ejection in which electric potential of the upper electrode is made to be higher than electric potential of the vibration plate as a lower electrode so as to deform the vibration plate to project toward the pressure chamber, thereby applying pressure to an ink in the pressure chamber so that the ink is discharged from a nozzle.
In the ink-jet head described in FIG. 3 of U.S. Patent Application Publication No. US 2005/0068376 A1 (corresponding to FIG. 3 of Japanese Patent Application Laid-open No. 2005-125743), in addition to the pushing ejection described above, it is also possible to perform a so-called pulling ejection. In other words, by making the electric potential of the upper electrode to be higher than the electric potential of the vibration plate in advance, thereby deforming the vibration plate to project toward the pressure chamber, and every time when there is a demand for ink discharge, the vibration plate is first made to return to its original shape (recover from the deformation), and then the vibration plate is deformed once again at a predetermined timing, thereby making it possible to discharge the ink from the nozzle. In such a pulling ejection, by deforming the vibration plate once again to project toward the pressure chamber at a timing when a negative pressure wave, generated when the deformed vibration plate is returned to its original shape, turns to positive pressure wave, it is possible to superpose this pressure wave and the positive pressure wave, thereby making it possible to apply, to the ink in the pressure chamber, a pressure greater than a pressure in a case of the pushing ejection. Therefore, by performing the pulling ejection, it is possible to drive the ink-jet head at a low voltage than by performing the pushing ejection.
For performing a pulling ejection in the ink-jet head described in FIG. 3 of U.S. Patent Application Publication No. US 2005/0068376 A1, however, it is necessary to maintain the upper electrode at an electric potential higher than an electric potential of the vibration plate all the time when ink is not discharged, and to continue to apply an electric field in the piezoelectric layer. Therefore, there is a fear that the durability of a piezoelectric layer is declined. Further, electric power consumption is also increased.
On the other hand, an ink-jet head, described in U.S. Pat. No. 6,971,738 (corresponding to Japanese Patent Application Laid-open No. 2004-166463), includes a channel unit in which a plurality of pressure chambers is formed, and a piezoelectric actuator having a plurality of piezoelectric sheets and individual electrodes (drive electrodes) and common electrodes arranged alternately between these piezoelectric sheets. The individual electrodes and the common electrodes are formed to overlap with one of the pressure chambers and to have a ring shape (annular shape) along an edge of the pressure chamber as viewed form a direction orthogonal to plane of the piezoelectric sheet.
Further, in this piezoelectric actuator, when a drive voltage is applied to the individual electrodes with the common electrodes kept at a ground electric potential, the piezoelectric sheets are deformed to project toward a side opposite to the pressure chamber. Therefore, it is possible to perform the pulling ejection as described above. Furthermore, in this case, it is enough that the drive voltage is applied to the individual electrodes only at timing when the ink is discharged. Consequently, the electric field is not applied to the piezoelectric sheets except for the timing of ink discharge, and thus polarization is hardly degraded in the piezoelectric sheets. Therefore, there is an advantage that durability of the actuator is enhanced.
However, in this piezoelectric actuator, due to a problem of a cross talk and/or the like, a wiring connecting each of the individual electrodes and a driver IC is formed in an area, on a surface of the uppermost piezoelectric sheet, which does not overlap with any of the individual electrodes. Here, each of the individual electrodes has a size such that the individual electrode substantially overlaps in a plan view with one of the pressure chambers. Accordingly, the area on the surface of the uppermost piezoelectric sheet, in which the wiring may be formed, is substantially limited to an area which does not overlap with any of the pressure chambers. Therefore, when the pressure chambers are to be arranged highly densely, drawing of the wiring connecting each of the individual electrodes and the driver IC becomes very difficult. Particularly, when the pressure chambers are to be arranged in a large number of rows, for example, in not less than three rows, the drawing of the wiring from an individual electrode corresponding to a pressure chamber arranged in an inner row among the rows becomes problematic. In such a situation, so far, a method of using a wiring member such as an FPC was adopted in many cases. However, this method lacks reliability of mechanical connection because the strength of connections is very weak.